In this example, is passed through this?

Question

In this example, is passed through this?

Good day! I am new to JS.
Here here , the following piece of code:

selectorMatches function(el, selector) {
 var p = Element.prototype;
 var f = p.matches || p.webkitMatchesSelector || p.mozMatchesSelector || p.msMatchesSelector || function(s) {
 return [].indexOf.call(document.querySelectorAll(s), this) !== -1;
};
 return f.call(el, selector);
}

I understand that .call first passed parameter indicates the context.
That is, in the end

return [].indexOf.call(document.querySelectorAll(s), this) !== -1;

will be

return document.querySelectorAll(s).IndexOf(this) !== -1;

But how this correlates with the very challenge in line with the return f.call(element, selector);?
As the context is transferred to element be used? and isn't that a simple analogue querySelectorAll(selector) get?

JavaScript

nikita.Stracke asked June 8th 19 at 17:03

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1 answer

rhoda_Dani answered on · Accepted Answer · 2019-06-08T15:05:32.546Z

You got that right, for ideas

[].indexOf.call(document.querySelectorAll(s), this)

what
document.querySelectorAll(s).indexOf(this)

But document.querySelectorAll() returns a collection of type NodeList and is not the same as Array, so it does not have its own indexOf () method. So structure [].indexOf.call(document.querySelectorAll(s), this) - this is a tricky way to do indexOf on an object which has no method indexOf. I suspect that somewhere in the bowels of the indexOf() turns this into an array by using Array.from(). This can be seen, for example, having "1" when execution of [].indexOf.call('abc', 'b') and "-1" when performing [].indexOf.call(1, 1).

Good initial design can be rewritten in

Array.from(document.querySelectorAll(s)).indexOf(this)

Then it will cause less questions.